Ken Gunnells, Ph.D. - Networking Paul Crigler - Programming IS 591 Introduction to Networking and Computer Programming University of Alabama at Birmingham Ken Gunnells, Ph.D. - Networking Paul Crigler - Programming Chapter 4: Data Link Layer Chapter 5: Network and Transport Layers Chapter 6: Wired and Wireless LANS

Student Discussion Are there any unanswered questions from last week? Have you acquired Visual Studio? Have you made arrangements for the programming book? Have you selected and gotten approval for your research paper topic? IS 591 - Week 2

Chapter 4 Data Link Layer Network Layer Data Link Layer Physical Layer

Data Link Layer Overview Controls what and when computers transmit Typically (in PCs) combined with the Physical layer below in a Network Interface Card (NIC). Card includes software for both layers + media port Formats data for the attached media Ethernet WiFi Fiber Optics Organizes incoming Bit streams for Network Layer above Detects and Corrects errors IS 591 - Week 2

Media Access Control (MAC) MAC controls when and what computers transmit If 2 computers want to talk at same time, MAC handles contention control or collisions. Two possible approaches Contention based access (e.g. Ethernet): allow collisions and follow rules for how to recover from a collision Controlled access (e.g. Token Ring, FDDI): prevent collisions by passing token to allow computer to talk Contention better for smaller networks <20 Controlled Access better for larger networks IS 591 - Week 2

Error Detection Sender calculates an Error Detection Value (EDV) and transmits it along with data Receiver recalculates EDV and checks it against the received EDV Mathematical calculations Mathematical calculations ? = Data to be transmitted EDV If the same  No errors in transmission If different  Error(s) in transmission Larger the size, better error detection (but lower efficiency) Parity checks Checksum Cyclic Redundancy Check (CRC) IS 591 - Week 2

Error Correction Once detected, the error must be corrected Error correction technique options… Retransmission: Receiver asks sender to retransmit message Simplest, most effective, least expensive, most commonly used Often called Automatic Repeat reQuest (ARQ) Forward Error Correction Receiving device can correct incoming messages without retransmission Requires extra information to correct IS 591 - Week 2

Network and Transport Layers Chapter 5 Network and Transport Layers Application Layer Transport Layer Network Layer Data Link Layer

Network and Transport Layers Transport and Network layers typically tied together as TCP/IP protocol Responsible for moving messages from end-to-end in a network Transport Layer: Responsible for segmentation and reassembly Breaking the message into several smaller pieces at the sending end Reconstructing the original message into a single whole at the receiving end Network Layer: Responsible for addressing & routing of messages Performs encapsulation on the sending end and decapsulation on receiving end Application Layer Transport Layer Network Layer Transport Layer Network Layer Data Link Layer IS 591 - Week 2

TCP/IP’s 5-Layer Network Model IS 591 - Week 2

Transmission Control Protocol (TCP) Internet Protocol (IP) TCP: Links the application layer to the network layer Performs packetization and reassembly Breaks up a large message into smaller packets Numbers the packets Reassembles the packets at the destination end IP: Responsible for addressing and routing of packets Two versions of Internet addresses in use IPv4: a 192 bit (24 byte) header, uses 32 bit addresses. IPv6: Mainly developed to increase IP address space (128 bit addresses) IS 591 - Week 2

Addresses at Different Layers Application Layer address (URL) e.g. www.UAB.edu Typed in a browser by user or clicked on a link Transport Layer: Breaks up outgoing and reassembles incoming messages, numbers packets Network Layer Address (IP address): 138.26.26.133 Retrieved from cache or Looked up using Domain Name Service (DNS) www.uab.edu resolves to 138.26.26.133 DNS service provided through a series of name servers Data Link Layer Address (MAC address):08:00:69:02:01:FC Adds unique MAC address to each packet to identify originating device Physical layer formats each packet for the media that is connected (electrical pulse, light pulse, radio wave) IS 591 - Week 2

Wired and Wireless Local Area Networks Chapter 6 Wired and Wireless Local Area Networks

Wired and Wireless LAN Overview Purpose of a LAN Sharing Information (files, database access) Sharing resources (hardware, software) Components of a LAN Network Interface Cards Cables (shielded/unshielded twisted pair, optical fiber) Hubs and Switches Connects cables from several computers Allows different media to connect (UTP,Coax) IS 591 - Week 2

Wired Ethernet Used by almost all LANs today 2 Types of Ethernet Shared Ethernet (Uses hubs) Shared central cable (bus). Collisions allowed Each computer see all messages, but only responds to messages with its address IS 591 - Week 2

Wired Ethernet Switched Ethernet (Uses Switches, no collisions) Logical and physical topology is a star via switch Switch reads destination address of the packet and only sends it to the corresponding port Forwarding tables: Switch reads the Layer 2 data link destination (MAC) address and sends frame out of the corresponding port in its forwarding table. Without collisions, network performance goes from 50% to 95% Port 1 Port 4 Port 2 00-22-69-13-EA-3E Port 3 Forwarding Table MAC Port 00-22-69-13-EA-3E 1 00-22-69-13-EA-3A 2 00-22-69-13-EA-01 3 00-22-69-13-EA-6C 4 00-22-69-13-EA-3A 00-22-69-13-EA-6C 00-22-69-13-EA-01 IS 591 - Week 2

Wireless Ethernet Use radio frequencies to transmit signals through the air (instead of cables) Two unlicensed frequency ranges 2.4 GHz (shared with cordless phones, baby monitors) 5 GHz Distance range of 100-150 meters, dependent on frequency Separate Channels reduce interference IS 591 - Week 2

End Questions? IS 591 - Week 2